Re: The ultimate Idaho weight \"smokin fur\" rifle
I really can not add much to what Shawn has already stated. Its kind of funny about the load development of all my Allen Magnums. Most of them are at the top of the pile in their respective caliber families so starting loads are not in print anywhere, so, I would simply estimate a very conservative starting load and load one round there and increase the powder charge one grain at a time for a total of 12 to 15 steps up in powder charge.
I would shoot the rounds on paper over a chrono at 100 yards and do the same as Shawn, watching for pressure signs. This is a quick and easy way to learn the upper and lower peramiters of a certain wildcat without using extensive amounts of time, componants and limiting barrel wear.
I will admit, I would load to the point of primer pocket loosening and then reduce the powder charge at least 2 full grains of back off to the point where the primer pockets on the fired cases felt no different then unfired pockets.
In nearly every case with all the Allen Magnums, I would take this "max working load" and load up 15 to 20 rounds and head out to 300 yards and shoot some groups just to check accuracy. So far, I have not had to return to the loading bench for more testing as all loads have produced 1/2 or better moa groups at 300 yards with this "Max working load" load.
Then I would load up 50 rounds, set the scope where I wanted for 300 yard impact, develope a ballistic drop chart and head to the long range shooting to test the drop chart.
With the 338 AM I developed loads for two different rifles, Black Sunshine, my 60 lb heavy rifle that I used this summer to get the Varmint Hunters Grand Slam with three chuck kills at 1095, 2100 and 2370 yards.
In that rifle, I started using H-50BMG and was very happy with the results. I started at around 130 gr and worked up to a top working load of 146.0 gr which produced a legit 3500 fps in the 40" barrel but pressures were pretty high resulting in loose primer pockets after the third firing.
I then backed that load off to 142.0 gr which produced 3420 fps with MUCH lower pressures.
After that, I decided to give the new US869 powder a try and with a starting load of 130.0 gr I was getting pretty severe hang fires. I cranked up the powder charge until this powder pressured out at 143.0 gr and 3460 fps. My lot of US869 was significantly faster burning then H-50BMG and I topped out in pressure with less powder.
I backed that load off to 138.0 gr which produced 3390 fps with VERY mild pressures again.
Both loads would easily hold 1/2 moa out to 1500 yards easily and I would say under 3/4 moa at well over 2000 yards.
I recently shot that US869 load in much cooler temperatures and found that it is very temp sensitive so I have now decided as Shawn has that for the time being H-50BMG is the most useful for the 300 gr class bullets.
I also gave Vhita Vouri 20N29 powder a try and will admit it worked very well with near 100% load density with comfortable pressures. I can not say it offers much more then H-50BMG does with the 300 gr pill but I have some more testing to do with the 350 gr ULD RBBT and Richard is working on some REALLY heavy 338 bullets where this ultra slow burning powder may just be THE powder for the big 338 AM. More testing this spring.
The second rifle I tested was a recent build with a 34" Lilja barrel. With this rifle top working loads were in the 3400 fps level with H-50BMG and the 300 gr SMK and 3375 fps was REALLY comfortable pressure wise.
All in all, from my testing and what Shawn has reported, it looks like you can expect the following velocity for the given barrel lengths using the 300 gr SMK and H-50BMG:
32" barrel...............3300-3350 fps
35" barrel...............3350-3400 fps
38 to 40" barrel.........3450-3475 fps
There will be several more rifles in this caliber made soon as I have 8 on order currently as well as two for myself ranging from 16 lb lightweights to 70 lb monsters with barrels from 32" up to 40" and pretty much everything inbetween.
I will also say that from what I have seen so far. It looks like the Lilja 338 barrels are running a bit slow compared to some other barrel brands but accuracy can not be complained about in any way.
Much more playing and reporting to come as well as alot of new bullet weights will be tried ranging from 280 gr up to possibly as heavy as 400 gr.
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